Spiders Feel The Electricity In The Air - And Use It To Fly

Spiders use global electrical fields to fly hundreds of miles without wings, according to new research.

The mystery of how wingless arachnids can go airborne for miles and miles has intrigued scientists for decades. Even Charles Darwin mused with delight on the topic when he saw hundreds of tiny spiders alight on the HMS Beagle as the ship was on its way to Buenos Aires.

Many scientists have suggested that spiders might achieve their aerial acrobatics by “ballooning” – spinning trails of silk that are caught on the wind to bear them aloft.

But spiders have been observed taking off when there is no wind at all, when it’s raining and when the sky is overcast. In the absence of wind, researchers have conjecture that perhaps spiders are riding on electrical currents in the atmosphere and a new study led by Bristol University backs this up.

“Many spiders balloon using multiple strands of silk that splay out in a fan-like shape, which suggests that there must be a repelling electrostatic force involved,” explained lead researcher Dr Erica Morley, an expert in sensory biophysics, in a statement.

“Current theories fail to predict patterns in spider ballooning using wind alone as the driver. Why is it that some days there are large numbers that take to the air, while other days no spiders will attempt to balloon at all? We wanted to find out whether there were other external forces as well as aerodynamic drag that could trigger ballooning and what sensory system they might use to detect this stimulus.”

The Atmospheric Potential Gradient (APG) is a global electric circuit that is always present in the atmosphere and insects have already been shown to use it. Bees, for example, can use their charge to communicate with their hive and bumblebees can detect the electric field (e-field) imparted by the APG to flowers.

In their lab, the researchers exposed spiders to controlled e-fields equivalent to atmospheric ones and by the simple experiment of switching them on and off, observed that spiders were using them to fly in the absence of wind.

“Previously, drag forces from wind or thermals were thought responsible for this mode of dispersal, but we show that electric fields, at strengths found in the atmosphere, can trigger ballooning and provide lift in the absence of any air movement. This means that electric fields as well as drag could provide the forces needed for spider ballooning dispersal in nature,” said Morley.

Spiders aren’t the only wingless insects that fly. Both caterpillars and spider-mites use aerial dispersal as a crucial biological process as well, making understanding that process important for understanding population dynamics, species distribution and ecological resilience.

“The next step will involve looking to see whether other animals also detect and use electric fields in ballooning. We also hope to carry out further investigations into the physical properties of ballooning silk and carry out ballooning studies in the field,” Morley said.